This invention relates to an automatic flush bolt mechanism for latching the inactive door of a pair of swinging doors.
Flush bolts are commonly used in pairs to latch the inactive door at the top and bottom thereof. The bolts of these mechanisms, when retracted, are flush or substantially flush with the respective upper and lower edges of the inactive door. When the bolts are projected, the bottom bolt engages with a strike plate located in the door sill or floor, while the top bolt engages with a strike plate located in the door frame above the door. Such door and flush bolt installation are shown in FIG. 12 of U.S. Pat. No. 3,578,369.
When the inactive door is in the closed position, the closing of the active door depresses the triggers of these mechanisms and thereby causes the bolts to project into their respective strike plates thereby securing the inactive door in a locked position. When the active door is opened, the bolts retract out of their respective strike plates and the inactive door is free to open.
A number of flush bolt mechanisms adapted to be mounted and employed on one of a pair of hinged doors have exhibited in various forms one or more characteristics which are desirable of such a bolt mechanism and which are incoporated into the present invention. Among such characteristics, the bolt mechanism should be capable of heavy-duty use and should be relatively easy to assemble and install. The bolt mechanism should provide a mechanism which will prevent the bolt mechanism from being damaged if the bolt and strike plate are not in alignment when the bolt mechanism is activated. It is also desirable to provide means for preventing the retraction of the bolt when the bolt mechanism is subject to heat in case of fire. Naturally, the bolt mechanism should provide for efficient activation of the mechanism and efficient projection and retraction of the bolt.
Automatic flush bolts are well known in the art. An example is shown in U.S. Pat. No. 3,578,369, assigned to the assignee of this application, in which the bolt is driven by rotation of a shaft activated by a pivotally mounted cam gear. Additionally, other flush bolts such as shown in U.S. Pat. No. 4,005,886 are operated by the presence of a second drive shaft which is operated by a pivotally mounted cam. This second drive shaft imparts sliding motion to the first shaft through a spring and thereby projects the bolt. In U.S. Pat. No. 4,099,753, provision is made for such occurrences by the use of a floating toggle which permits a pivot pin for the toggle arm to move and prevent extension of the bolt if there is misalignment. This tends to complicate an otherwise simple mechanism and results in lack of a direct drive.
In the present invention, a direct toggle drive for a flush bolt is provided, together with an intermediate connection between the drive mechanism and the bolt mechanism, which is relatively stiff in a direct drive mode but which is resilient and protects the bolt assembly in the event of misalignment of the extensible bolt with the strike plate.
The present invention represents an advancement over prior bolt mechanisms by virtue of a less complex and highly efficient override structure to prevent damage from misalignment and by virtue of the efficient translational motion of the bolt mechanism. Moreover, the present invention provides a bolt mechanism which is relatively easy to assemble, and by virtue of its unique construction and operation, provides a bolt mechanism which is adaptable for heavy-duty use.